1. Field of the Invention
The present invention relates to an internal combustion engine with a cam phase change mechanism capable of changing the phase of an intake cam.
2. Description of the Related Art
Conventionally, there are internal combustion engines that comprise a cam phase change mechanism as a variable valve gear, which changes the phase of an intake cam to vary the opening and closing timings of an intake valve. Further, a technique has been developed in which the cam phase change mechanism is applied to internal combustion engines that are provided with a plurality of intake valves for each cylinder. According to this technique, the opening and closing timings of only some of the intake valves are varied in accordance with the load and engine speed.
In one such internal combustion engine, the opening and closing timings of some of the intake valves are delayed in, for example, low-load operation so that the open period of the intake valves as a whole is increased toward the delay-angle side, whereby a pumping loss is mitigated (Jpn. Pat. Appln. KOKAI Publication No. 3-202602).
However, the technique described in the above patent document has a problem that a valve train is inevitably large-sized, since two camshafts for driving the intake valves are arranged laterally relative to the internal combustion engine.
In order to improve combustibility, moreover, it is advisable to vary the opening timing of each intake valve independently of the closing timing. While the closing timing of the intake valve, in particular, should preferably be widely variable, the valve-opening timing needs only to be slightly variable. As in the technique described in the above patent document, on the other hand, it is difficult for a single cam phase change mechanism to properly control both the opening and closing timings of intake valves with different necessary variable ranges.